The present invention relates to a process for the separation of carbon dioxide and hydrogen sulfide from gases using a promoted methyldiethanolamine (MDEA) solution.
The scrubbing of sour gases, i.e. gases containing carbon dioxide and/or hydrogen sulfide, is widely practiced in the oil and gas industry. One family of scrubbing liquids includes aqueous compositions that contain amines. For instance, it is common to employ scrubbing liquids containing tertiary amines, such as methyldiethanolamine (MDEA).
For a variety of reasons, scrubbing liquids containing MDEA have had primary amines, such as monoethanol amine (MEA), added thereto. It is perceived that addition of certain amounts of MEA enhances the scrubbing capacity of MDEA liquids, without seriously undermining the advantages of the MDEA (e.g., facile deabsorption of sour gas).
Another primary amine which has been discussed previously for use in conjunction with MDEA is 2-(2-aminoethoxy)ethanol. 2-(2-aminoethoxy)ethanol is available commercially at the present time from Huntsman Corporation under the trademarks DIGLYCOL AMINE.RTM. and DGA.RTM..
However, it is also known that DIGLYCOL AMINE.RTM. brand 2-(2-aminoethoxy)ethanol, when used alone in aqueous or non-aqueous scrubbing liquids, degrades to form bis-(2-hydroxyethoxyethyl)urea (BHEEU). BHEEU is ineffective in removing the acid gas impurities from the sour gas. Thus, DIGLYCOL AMINE.RTM. brand 2-(2-aminoethoxy)ethanol must be replaced or regenerated periodically to retain efficiency. Regeneration is commonly performed in a reclamation unit, in which the urea is heated. Such reclamation units are costly and thereby add a disincentive to end users from employing scrubbing solutions based on DIGLYCOL AMINE.RTM. brand 2-(2-aminoethoxy)ethanol.
In view of this background, the industry has been adverse to using DIGLYCOL AMINE.RTM. brand 2-(2-aminoethoxy)ethanol as an alternative primary amine, as opposed to MEA, in conjunction with MDEA. That is, due to the known degradation of DIGLYCOL AMINE.RTM. brand 2-(2-aminoethoxy)ethanol, the industry has been led away from employing MDEA and DIGLYCOL AMINE.RTM. brand 2-(2-aminoethoxy)ethanol.
It can thus be seen that a need exists for a DIGLYCOL AMINE.RTM. brand 2-(2-aminoethoxy)ethanol promoted MDEA scrubbing liquid which overcomes the problems identified above. It would be advantageous to possess a DIGLYCOL AMINE.RTM. brand 2-(2-aminoethoxy)ethanol promoted MDEA liquid that does not require regeneration by way of a reclamation unit, for instance.